It has become a serious consideration in the lumber industry to improve grading of lumber and therefore improve secondary breakdown decisions. By optimizing the recovery of"good wood" against a slate of desired products, the value of the lumber may be increased. "Good wood" refers to wood which meets a prescribed criteria. For different uses, what is considered "good wood" may vary. For example, for fine furniture, it may not be acceptable to have any knots in the wood. However, for furniture intended to have a more rustic appearance, a certain number of knots may in fact be desirable. In general though it is desirable to identify certain "defects" in the lumber, and to locate them with respect to a spatial reference system. One method of doing this is to have a human visually inspect each piece of lumber prior to it being cut into secondary boards. This is slow and prone to error. Further, even if the defect is identified, the information must still somehow be communicated to a saw operator in a meaningful manner to allow the defect to be isolated, yet allow wood recovery to be optimized against a desired product slate.
There have been some improvements in the area of grading lumber, for example Lumber Optimizer (U.S. Pat. No. 4,879,753 to Aune et al), Method of Estimating the Strength of Wood (U.S. Pat. No. 4,941,357 to Schajer), Dielectric Sensor Apparatus (U.S. Pat. No. 5,654,643 to Bechtel et al), Detector for Heterogeneous Materials (U.S. Pat. No. 5,585,732 to Steele et al), and Flaw Detection System Using Microwaves (U.S. Pat. No. 4,514,680 to Heikkila et al) which uses microwaves to measure lumber flaws.
Defects comprise such features as knots, rot, splits, sap, skips, holes, cracks, wane, stain and the like. Defects may be further subclassified, for example a knot may be a sound knot or an unsound knot. Most defects have some attribute which allows them to be detected by automated scanning. For example, reflective inspection (laser or gray-scale video) can detect stain and sap in wood. Transmissive inspection techniques (such as x-ray) can detect density variations, and thus knots and rot and the like. As indicated, a variety of automatic inspection techniques exist for determining the presence of such defects. Most of these methods give only an indication of the probability of a defect, and do not guarantee that the object identified by the inspection technique is actually a defect. However, by combining the different results of automatic inspection into a single model, defects can be verified and the probability that an identified object is in fact a defect are increased. Further, combining inspection results allows further characterization of a defect. For example, a dark area identified by a visual scan can either indicate rot, stain, or a knot. However, verification of the visual scan with an x-ray scan can reveal the object to be rot if the x-ray scan indicates it is an area of low density, or a knot if the x-ray scan indicates it is an area of high density.
It is desirable if all of the results of inspection can be combined to produce a board model, which in the digital realm might be more appropriately termed a "virtual board." The board model can then be analyzed for optimum yield against a product slate. Further, automated handling machines such as conveyors, and automated process machines such as saws, can control the handling and processing of the physical board on which the board model is based.
It is further desirable to have a system which is flexible and can easily accommodate the addition or subtraction of additional components, such as additional inspection subsystems, user interfaces, computer controlled machines (saws, etc.), and additional technology as it becomes available.
For any such system to be effective, it is desirable that the system be able to determine the precise location of the board at various points throughout the system. Various prior art tracking systems such encoder wheels can become inaccurate due to slippage, and can cause undesirable marking of the product in the event of a failure. It is therefore desirable to provide a tracking system which is accurate and reliable.